The instant invention is directed to a process for fabricating articles (e.g. bottles, stamped plastic sheets, rigid foams, etc.) from specific thermoplastic compositions. These compositions are either multiphase resinous copolymers having certain critical characteristics or specific ionomeric polymers (ionomers) as more fully described hereafter. This fabrication process allows production of articles which, on simple heating, change their shapes to form a predetermined new configuration. Thus, for example, a sheet or compacted slab of material prepared by this novel process can be simply heated by the ultimate user to form a container or a rigid foam without the necessity for him to employ costly molds, etc.
It is known that crystalline and semicrystalline polyethylene and copolymers thereof with propylene may be used to prepare fabricated articles by a process in which the polyethylene is formed as a molded object, permanently crosslinked by either chemical means or by irradiation, then heated to about 140.degree. C. and collapsed and cooled. Reheating to the temperature at which the object collapsed restores the original shape. See U.S. Pat. No. 3,563,973 and 3,526,683. While that fabrication process has obvious advantages there are also several serious disadvantages. Both chemical and radiation crosslinking are expensive operations and increase the cost of the final product. Further, crosslinking is irreversible, i.e., once polyethylene is crosslinked, it cannot be returned to the uncrosslinked state. Therefore, it is impossible to reuse scrap. Since the process is limited to only polyethylene and certain of its copolymers, strict limitations are placed on applicability of the final product. For example, certain critical temperatures must not be exceeded, etc. By contrast, the process of the instant invention employing the thermoplastic compositions more fully described hereafter achieves all the advantages of the above-described prior art process and avoids all of the disadvantages attendant thereto.
French Pat. No. 1,576,598 broadly discloses multiphase polymers which may be random, block or graft copolymers wherein either both monomers would produce a resinous homopolymer or one would produce a resinous and one an elastomeric homopolymer. For purposes of the instant invention, it has been discovered that random copolymers and copolymers wherein any monomer unit would produce an elastomeric polymer are not applicable. In fact, the only polymers applicable to the instant invention are either thermoplastic ionomers as more fully described hereafter, or graft or block copolymers falling within the following general structural formulae: